Pipe connection arrangements of the type in question are known especially in connection with high-pressure gas lines, in which pipe conduit elements are connected to one another by a screwed joint or to connection stub elements of a combustion engine, in particular a dual fuel engine.
It has been found that these screwed joints can begin to leak. As a result, fuels, such as gas or oil, can escape in an uncontrolled manner from a corresponding fluid line system, in particular from a high-pressure fluid line system, and cause damage.
In order to prevent the risk of such unintentional loosening of the screwed joints, a cone clamping system is used, which is integrated into the union nut of the screwed joint. In this cone clamping system, the ends of the pipe conduit elements or of the connection stub elements are of conical configuration. In addition, the union nuts of the screwed joints are secured by means of a locknut system in order to increase the preload in the union nut. An illustrative description of such an embodiment from the prior art can be found in German Utility Model DE 91 06 441, for instance.
Moreover, there is often the problem that screwed joints of this kind are situated in areas of the system which are accessible only with difficulty, e.g. on a burner support flange of a gas turbine system, which is extremely difficult to reach from outside, thereby increasing the risk that such screwed joints will not be tightened properly.
A prior-art pipe connection arrangement 1 of the type in question for a high-pressure gas line system 2 of a dual fuel engine 3 comprising a gas turbine (not shown) is shown in FIG. 4. On the one hand, this pipe connection arrangement 1 has a pipe element 4 having a connection end 5, which comprises an outer sealing cone 6 and a conical shoulder 7. On the other hand, the pipe connection arrangement 1 has a further pipe element 8 in the form of a connection stub element 9 of the dual fuel engine 3, said element comprising an inner sealing cone 10 and an external thread 11 at the end. The pipe element 4 and the further pipe element 8 are inserted one into the other along a central longitudinal axis 12 of the pipe connection arrangement 1, with the result that the outer sealing cone 6 of the pipe element 4 rests in positive engagement on the inner sealing cone 10. Also inserted into the further pipe element 8 is an inner pipe component 13, wherein the inner pipe component 13 is spaced apart from the first pipe element 4 with a spacing 14, giving rise to a gap 15. A seal element 16 is inserted in the gap 15. The two pipe elements 4 and 8 of the pipe connection arrangement 1 are clamped to one another in the direction of the central longitudinal axis 12 by means of a screw nut element 17 in the form of a union nut 18. For this purpose, the union nut 18 is pushed onto the first pipe element 4 and screwed onto the external thread 11 of the further pipe element 8 by means of its internal thread 19. During this process, an inner clamping cone 20 of the union nut 18 comes into effective contact with the conical shoulder 7 of the first pipe element 4. The further the union nut 18 is screwed onto the further pipe element 8, the further the first pipe element 4 is taken along in the direction of the further pipe element 8 by the inner clamping cone 20 of the union nut 18 until, ultimately, the outer sealing cone 6 of the first pipe element 4 is clamped to the inner sealing cone 8 of the further pipe element 8 with the desired preloading force. The pipe connection arrangement 1 is furthermore fixed on a burner support flange 22 by means of a bulkhead union 21, wherein the further pipe element 8 is passed through a bore 23 in the burner support flange 22. The bulkhead union 21 comprises a nut 24, which is likewise screwed onto the external thread 11 of the further pipe element 8. The further pipe element 8 has a shoulder 25, against which the burner support flange 22 is clamped by means of the nut 24. The pipe connection arrangement 1 known from the prior art and shown in FIG. 4 is thus embodied as a cone clamping system 26 with a screwed joint (union nut), wherein good leaktightness can be achieved by virtue of the preloading force introduced into the pipe connection arrangement 1 by the union nut 18.
In general, the components of such screwed joints remain connected to one another firmly and therefore also leaktightly as long as the cone clamping system 26, in particular the outer sealing cone 6 and the inner sealing cone 10 thereof, and the union nut 18 are at approximately the same temperature. This is the case especially when a corresponding system is being operated in the steady-state mode.
However, relatively large temperature fluctuations can occur briefly, especially in dual fuel engines 3, if a change of fuel is carried out, i.e. there is a switch between a supply of oil and a supply of gas. Owing to the fact that transiently cold gas is briefly introduced through a pipe connection arrangement of the type in question for a fuel line, the cone clamping system 26, in particular the outer sealing cone 6 and inner sealing cone 10 thereof, can cool down by a critical amount and contract in such a way that the preload of the union nut 18, which is still warmer, is not sufficiently high to keep the outer sealing cone 6 and the inner sealing cone 10 compressed axially to give a sufficient sealing action. The screwed joint is simply loosened and leaks 27 occur. In combination with vibrations in the system, e.g. those due to less smooth combustion, the pipe connection arrangement 1 may become even looser due to shaking, with the result that it may still be leaky even when the prevailing temperature conditions at said arrangement are once again uniform.